Page:Popular Science Monthly Volume 16.djvu/205

 of the data is complete for the part of the ocean under consideration. The final step is to arrange the matter in shape for the engraver and printer. This is done on sheets of Form C—a blank eight inches by ten—which is a facsimile of one of the squares of the monthly charts enlarged to a size suitable for writing all the data in the proper spaces. The data for all the squares for one month are transcribed from Form D to Form C; these are sent to the engraver; a proof-sheet comes back in due time; this is read and corrected; and eventually the charts themselves issue complete from the press. Until the year 1876 no systematic use was made of the log-books of our vessels of war. Every six months they were sent from each squadron to the Navy Department, where they have been accumulating since the days when Maury had the supply then on hand compiled for his charts.

Now, a large number await examination—a rich mine of valuable material. A set of charts for the Pacific Ocean between the equator and latitude 45° north, and from the American coast to the 180th meridian, are the first fruits of labor in this mine. The complete set consists of fifteen different sheets: 1. Twelve on which the information peculiar to each month is given on a separate sheet; 2. One that summarizes all the observations of the direction and force of the wind of every month and year; 3. One that similarly gives all the observations of the barometer, thermometer, and weather; and, 4. One in colors showing the wind systems, stormy regions, and areas of equal heat and equal pressure—a graphical exhibit of what the other charts contain.

Preceding the set are, a table giving for every month the latitude and longitude in which each ship entered or lost the trade-winds; a list of the log-books whose data enter into the charts; and a preface chiefly descriptive of the method of compilation. All are printed on thick paper and bound together in a folio volume convenient for use.